In electrography, image charge patterns are formed on a support and are developed by treatment with an electrographic developer containing marking particles which are attracted to the charge patterns. These particles are called toner particles or, collectively, toner. Two major types of developers, dry and liquid, are employed in the development of the charge patterns.
In electrostatography, the image charge pattern, also referred to as an electrostatic latent image, is formed on an insulative surface of an electrostatographic element by any of a variety of methods. For example, the electrostatic latent image may be formed electrophotographically, by imagewise photoinduced dissipation of the strength of portions of an electrostatic field of uniform strength previously formed on the surface of an electrophotographic element comprising a photoconductive layer and an electrically conductive substrate. Alternatively, the electrostatic latent image may be formed by direct electrical formation of an electrostatic field pattern on a surface of a dielectric material.
One well-known type of electrostatographic developer comprises a dry mixture of toner particles and carrier particles. Developers of this type are employed in cascade and magnetic brush electrostatographic development processes. The toner particles and carrier particles differ triboelectrically such that, during mixing to form the developer, the toner particles acquire a charge of one polarity and the carrier particles acquire a charge of the opposite polarity. The opposite charges cause the toner particles to cling to the carrier particles. During development, the electrostatic forces of the latent image, sometimes in combination with an additional applied field, attract the toner particles. The toner particles are pulled away from the carrier particles and become electrostatically attached, in imagewise relation, to the latent image bearing surface. The resultant toner image can then be fixed, by application of heat or other known methods, depending upon the nature of the toner image and the surface, or can be transferred to another surface and then fixed.
Toner particles often include charge control agents, which, desirably, provide uniform net electrical charge to toner particles without reducing the adhesion of the toner to paper or other medium. Positive charge control agents impart a positive charge to toner particles in a developer; negative charge control agents impart a negative charge to the toner particles relative to the carrier particles.
U.S. Pat. No. 5,405,727, whose disclosure is incorporated herein by reference, describes N-(carbonyl, carbonimidoyl, and carbonothioyl) sulfonamide compounds as negative charge control agents in electrophotographic toners. Other types of negative charge control agents are described in U.S. Pat. Nos. 4,464,452; 4,480,021; and 5,186,736, the disclosures of which are incorporated herein by reference.
Many prior art negative charge control agents have a variety of shortcomings. For example, some are dark colored and cannot be readily used with pigmented toners such as cyan, magenta, yellow, red, blue, and green toner particles. In addition, some previously known charge control agents are highly toxic or produce highly toxic by-products, while others are highly sensitive to environmental conditions such as humidity. Still others exhibit high throw-off or adverse triboelectric properties under certain conditions of use. There is thus a continuing need for negative charge control agents having improved properties relative to those currently known in the art.
A general route leading to the formation of 4H-pyrans via the zinc chloride catalyzed condensation of .beta.-dicarbonyl compounds with aldehydes is described in J. Wolinsky and H. S. Hauer, J. Org. Chem, 1969, Vol. 34, No.10, page 3169. U.S. Pat. No. 5,760,073 describes the synthesis of substituted 4H-pyrans for use as active compounds in medicaments, in particular, for the treatment of the central nervous system. Their use in the field of electrostatographics, however, has until now been unknown.